Ladder type delay line



Jan. 5, 1960 o. DoHLr-:R ETAL LADDER TYPE DELAY LINE 6 Sheets-Sheet 1 Filed May 19, 1953 F Q u q Jan. 5, 1960 Filed May 19, 1953 LADDER TYPE DELAY LINE 6 Sheets-Sheet 2 Jan. 5,- 1960 o. DoHLl-:R l-:TAL` 2,920,227

LADDER TYPE DELAY LINE 6 Sheets-Sheet 3 Filed May 19. 1953 O. DOHLER ETAL LADDER TYPE DELAY LINE Jan. 5, -1960 e sheets-sneek 4 Filed May 19. 1955 .:lahwsww Jan. 5, 1960 o. DOHLER ETAL LADDER TYPE DELAY LINE 6 Sheets-Sheet 5 Filed May 19, 1953 E .mm1

Jan. 5, 1960 o. DoHLl-:R Erm.

LADDER TYPE DELAY LINE 6 Sheets-Sheet 6 Filed may 19, 195s United States Patent() C? LADDER TYPE DELAY LINE Oscar Dohler and Bernard Epsztein, Paris, France, as-

Ysignors to Compagnie Generale de Telegraphie Sans Fil, Paris, France v "f'Il'hepresent Yinvention relates to delaylinesof the ladder type, more particularly vfor use in travelingwave tubes and magnetrons.

" vThe presentrmventlon relates to a very Vparticular type lof delay line for use in electron discharge tubes operating by interaction between the energies oontaiuedrespectively inthe electron beam and in the iield of an ultra high frequency Ywave propagated along the line, as for example in .traveling wave tubes. This type of delay line fis constructed in the form of a ladder comprising two parallelv longitudinal lateral members and a series of parallel'rungsextended between the two lateral members, and a metallic base plate upon which the lateral members -are supportedn with the rungs spaced from the base-plate. The length of the rungs is approximately equal to half the operating wave length, and from this point Vof view the ladder type delay line operates more 'eiciently than the other known types of delay line suchvasinterdigital or baille lines. The defect of these other types of line lies in the fact that the width of the .line is only a quarter wave length or even less. Consequently, for equal length the ladder line may be used in a tubev the electron beam of which is very much 4wider and the beam current of which is more intense, whereby the tube can supply a greater power. Furthermore, the coupling resistance between the wave and the beam is high with consequent favorable inuence on the gainof the tube.

#Delay lines of ladder type are already known, however, which have the disadavantage of opposed electrical and' magnetic couplings as will be more fully explained hereinafter.

. The present invention has for its purpose to improve Y the known delay rlines of ladder type, the primary object .'being to increase' the band width and permit propagation Aof energy within a wide band of frequencies independently of irregularities in the construction ofthe line. The. principal 'feature of the present invention is the provision of means for tightening up the coupling between the individual circuits constituting the delay line.

. The invention will be more readily understood from thev ensuing description taken in conjunction with the accompanying drawing in which:

, Figure l is a perspc.tive view of a known delay line of ladder type;

lFigure 2 is a diagrammatic representation of a chain of circuits constituting a delay line of the type shown in VFigure 1;

. Figures 3 to 5 illustrate three forms of the invention Awherein means are provided for reducing the electrical Icoupling of a ladder type delay line;

Figure 6 is a graphicrepresentation of the dispersion n"curves ofthe lines illustrated in Figures 3 to 5;

Y Figures 7 to 9 and 11 illustrate four embodiments of the invention comprising means for decreasing the magnetic coupling; n Y l Figure l0 is a graphic representation of the dispersion curves of lines in accordance with Figures 7 to 9;

2,920,221 .Patented Jan. .5,1969

Figure 12 is a cross section through a crossed field traveling wave tube comprising a delayline in accordince with Figure 9; and

Figures 13 and 14 are respectively'anaxial section and a transverse cross section through a magnetron comprising a delay line in accordance with Figure 8 curved tocircularshape. E. Y. A

Referring to Figure' "the ladder `type, delay line of known construction comprises two longitudinal lateral members 1 and anseries of rungs 2 spanning the space between the lateral .mem-bers. The twov lateral 'mem'- bers are mounted on a metal base plate 3 andthe length ofthe rungs 2 is approximately M2, 7x being the operating wave length of the` line.

Figure 2 illustrates how the delay line of Figure 1 may be assimilated to a. chain of lter-type circuits having lumped constants. The dotted line 14 in Figure 1 comprising a rung 2 and the closed path along the walls of the lateral members 1 and'across the base plate 3V may be considered the equivalent of an anti-resonant vcircuit comprisinga coil L1 and a capacitor C1 tuned to M2. The distribution of potentials on each rung, as also' in eachhalfwave circuit, is suchv that the potential is zero at the extremities and maximum at the cen- `ter. ,.Consequently, in thecentral zone of the rung an electrical eld ofmaxiinum value iscoupled with `the electrical fields ofzfthe"neighboringrungs AThis coupling between* the electrical fields i's v,the equivalent of the capacitor C2 yof Figure"'2. 'Furthermore, a high kfrelquency current circulate's' through each' rung the distribution of which is such that it is high at the central zone of the rung and maximum 'at thefextremities. This current generates 'a maximum magnetic field at the extremities of the rung. which iscoupled to the magnetic fields of the Vneighboring rungs, ,This magnetic coupling is lthe equivalent of an inductive coupling 'shown on Figurel 2 as coils L2 and .Lgbetween the coils L1 of the successive circuits. Finally thedagrammatic showingof Figure 2 discloses a chainof'anti-resonant circuits coupled electrically by the capacitors C2 and magnetically by the Yinduction Circuits LaLal g :It Yis known that type ofchain the electrical and 'magnetic couplings are iriufually opposed so that :the resonant. coupling is 4very weak. v.It is also known thata chain of weakly coupled circuits has a very narrow rband-width and that fthe crcuitsmust be' very closely tuned to,.thenresonantffrequency. This phenomenon is repeated in the ladder type delay line of Figure l-. where the dispersion, i.e. theuvariation of the delay vfactorasa function of Vthe wave length, is very substantial, and wherethe slghtestirregularity of mechanical` structure 'involves discrepancies' between the resonantv frequencies ofthe individual. circuits of the chain. fI'he band width is Vinfact so `narrow that this property ofthe ladder type delay line sometimes prevents it from propagating' any electro-magnetic iield, whatsoever.

In Figure' 3, where .the 4same reference numerals designatethe same elements as in Figure l, the electrical Vcoupling between ,the successive rungs is decreased by inserting a lillerfmember i4 between the base plate 3 and thelgrungs 2.. The liller member 4 extends longitudinally 'ofthe delay line ,or'parallel to thelocus `of the rungs 2, thelevngth of the member 4 being greater'than either Athe :space between adjacent rungs, or the width 0f each rung has the eiect of 'deforming`fthe electrical field in 'the vicinity of the centralzones'ofjtherungs whereby ra portion of the lines of force is d'electfedy and redirected from` eachV rung toward 'the filler "member insteadv `of Ltoward thevnerighborin'g; rung. there 'is a'l Snll" number '.Qf @flares-"a e1' engedin .th trical c0up1ing. n fr, t u

In the embodiment according to Figure 4j battles 3 are positioned in the spaces between the rungs` 2, the width of Ythe'bziiiles 'being such as to extend over the central zones of the rungs. It will be readily understood iuthis ernhodimentdhe capacitoLCyI of Figurel is replaced f by two capacitors connected series, the. result being well known in that'it provides .a reduced .resultant capacity. Y f Figure .5 .discloses v.ac.ornbin:.1tion .f [theiiller member 4. o'f Figure i3 .and .of thebafles l5 .of .Figure .4.

`Decoupling'by means of batlles in accordance-with Figures 4 fand .5 .has the added advantage, lin traveling wave tubes .wherein .it fis .well known that .the .beam gradually bendslowardthe anode as it progresses -along fthe .interaction .space,.fthat .the [baies rather than .the rungs are exposed to .thestreamof electrons. Thus the electrons are absorbed'lby massiveelements which have a good heat dissipation. VThe upper surfaces of the baffles which are. exposed tothestream of electrons propagated inthe interaction space -.alQng.the delay lineare parallel Atothelocus 4of .therungs longitudinally of .the line aswell asparallelingfthe rungs,.transve'rsely ofthe line. .The disposition of the lla't Velectron'bearn along the delay line may be generally `the same as thatillustrate'd inFigure 12 with regard to thebase plate i3" arid the transversely extending rungs thereon which are described hereinafter. The electron beam thuspasses'in interacting relationship with the rungs on the side thereof opposite thebase plated. VThe electrical decoupling in accordancewith Figures 3 .to 5 is increasingly effective in that order, 'Figure 5 being the mosteffective.- Figure .6 is a graphic representation of the ratio "between the speed of light c and the phasepropagation velocity 'vph as a function of .the wave length A, from'whichitispossible to evaluate the dispersion. The curvel corresponds to vthe delay line of Figure'3 and lthe curves 2 and 3 to the delay line Yof Figure 5 wherein .the bafes 5 are of different heights. The straight line` 4 indicates the locus Yof the .cut-0E frequencies. The portions of the curves shown in full lines correspond 'to .a propagation at the highest .phase velocity .among Lthose which are feasible, and the portions shownin brokenjlines correspond to propagation with aphase velocity as close as possible to the maximum velocity of the preceding mode. It will be seen that the more effective is the electrical decoupling the weaker is the vdispersion and consequently the wider will be the band.

Figures '7 to 9 illustrate the three embodiments of Ythe invention wherein means areincorporated for decreasing 'themagnetic coupling, .the .charcteristic feature common to thesethreeembodiments beingthat the rungs are .divided into twogroups occupy-ing .alternate .odd .and even positions, the rungs of atleast one group being bent at right angles'and vthe extremities thereof being implanted in the surface ofa member .separate from that in which the ends of .the-other group are implanted.

In'Figure' 7, the .odd rungs '2' areconventional, whereas the Yeven rungs 2"..are .bentdownwardly .and their ends are implanted into 'the surface of elements 13 vdistinct from the surface .of the lateral membersl -in which the ends of the rungsZ are implanted.

4In Figure 8, both. groups .ofrungs .are bent at right angles, onevgroup havingftheir ,ends implanted in the upper levelof asteppedlateralmember 1 andthe .other group in thelower .level thereof, whereby the ends of the respective groups .are implantedin two distinct surfaces. 'The width .of .one group between the Vbent portions thereofjs dierentjfrom the .width of the rungs of the other groupfgbutlthe. overall length of veachrung is equal to approximately M2. f y

hIn Athe embodiment-g.shown @in ...Figure .9, :the rungs 12' .and 2".-are1hentover identieallyrhutain opposite. directions, thelateral members ...Land the;base.p1ate 3 being duplicated as' indicated respectivelyat 1' .1", and #3. 3'3

The magentic decoupling increase in eifectiveness from Figures 7 to 9 in that order, and Figure 10 is a graphic representation similar to that of Figure 6 showing the `dispersion curves 1, 2 and 3 corresponding respectively to the delay lines of Figures 7, 8 and 9. As in Figure 6 the straight line 4 indicates the locus of the cut-off frequencies, andthe portions shown Yrespectively in full, and in broken lines having the same signicance as in .Figure 6. It will be seen that the more elfective the magnetic decoupling the weaker the dispersion, .the slope of the curves ybeing gradually reduced and becoming more regular.

There are, of course, many other possibilities of magnetic decoupling, for example as shown in Figure l1 where bafes 5 are inserted between the end portions of the rungs, this arrangement being similar with respect to magnetic coupling to what is shown for electrical coupling in :Figure 4. In any event, not only in Figures 7 to 9 but also in Figure 11, decoupling is obtained by lengthening or complicating the path through Whichthe current circulating on the surface of the metal mass .short-circuiting the rungs would have to pass between the adjacent ends of two consecutive rungs.

The invention maybe applied in practice to many types of electron discharge tubes operating on the principle of interaction between a beam and a wave. Delay lines according to the invention are more particularly intended, however, for use in -traveling wave tubes wherein the interaction between the beam and the wave takes place within the range of crossed electrical and magnetic fields, these tubes operating as ampliers in accordance with one .mode of propagation wherein the phase velocity is of the same sign as the group velocity, or as oscillators in accordance with amode of propagation wherein the two -velocities 'have opposite signs. In Figure 6, the full line portions :of the curves decrease when the wave length increases which indicates that the phase velocity has the same sign as the group velocity for the mode of propagation .corresponding to those portions of the curves. The broken line portions increase on the contrary which corresponds to a phase velocity opposed to ythe group velocity. In .Figure 10, -on the contrary, the full `line portions increase andthe broken line portions rdecrease or aresubstantially horizontal. Consequently the delayv lines of which .the dispersion is indicated by the curves of Figures 6, i.e. .electrically uncoupled delay lines, may be used in crossed eld ltubes operating as amplifiers in accordance withy a mode of propagation the .phase velocity of which is vas v high as possible, or as oscillators in accordance witha YInode the phase Velocity of whichis lower than the highest possible Velocity. The delay lines of which the dispersion is given by Figure 10, i.e. magnetically uncoupled delay lines, Vmay be used in crossed eld tubes operating as oscillators in accordance with a mode of propagation at maximum vphase velocity, or as Vamplifiers in accordance with a mode of lower phase velocity.

Figure l2 illustrates by way of example va transverse section through a tube including a delay line in accordance with the present invention. The delay line is of the type illustrated in Figure 9, but it must be understood that-any other one of the lines described herein could be substituted without departing from the scope ofthe invention. In addition to the rungs 2 and 2 andthe plates i3 and 3" there are shown in Figure l2 the usual negative electrode 6, the electron beam 7 passing between the elec- "trode 6 and the delay line, side walls 8 mclosing `the tube, and magnetic poles l9.

The rectilinear shape ofthe tubeshown in Figure .l2 is yin no way intended kto limit the invention. On the contrary, the delay line may be bent to cylindricalshape for use in ycircular traveling Wave tubes.

property of low dispersion obtained with the;delay larly suitable vfor use in magnetronswithout theY necessity Furthermore Athe .successive rungs, the transverse said base plate facing for using the connections knownV as straps which are inserted for 1 artificially reducing the high dispersion of lmown anodes and for preventing the magnetron from Jumplng too easily from one frequency of oscillation to another. 'Ihe delay lines according to the present invention, having `a low dispersion and beingY comparable to a wide band' circuit, already prevent these frequency jumps without the use of straps. Y

v vFigures 1,3 and 14 are respectively an axial section and a cross'section through a magnetron using a delay line for example as in Figure 8 curved to circular shape, but it must be understood that any other line in accordance with the invention could be substituted. In these two figures, there are shown the rungs Z' and 2", the lateral members 1 and base plate 3 being rolled to cylindrical shape. In the axis of the magnetron is positioned a cathode 11 and the magnetic teld is produced by a coil 12.

What is claimed is:

l. A micro-wave delay line constructed and arranged for interaction with an electron beam propagated along said line in an adjacent interaction space, said delay line comprising at least one metal base plate, a pair of lateral members essentially .parallel to said-base plate and extending along the side edges thereof and a series of essentially parallel rungs extending between the two lateral members and of a length approximating one half the length of the wave to be delayed by the line, said lateral members being mounted so as to suspend said rungs in spaced relationship to said base plate on one side thereof between the plate and said interaction space, said line being electrically equivalent to a chain of coupled circuits including both electrical coupling and magnetic coupling,

and conducting means comprising at least one conducting small value with respect to said magnetic coupling, said conducting member having a surface arranged to be exposed to said electron beam propagated along said line on the side of said rungs opposite said base plate, said surface extending parallel to said rungs transversely of said line as well as extending generally parallel to the locus of said rungs longitudinally of said line. V

6. In a magnetron tube comprising an envelope, a delay line for micro-waves inside said envelope, said delay line being so constructed and arranged as to Iinteract with an electron beam propagated along said line in an adjacent interaction space and comprising a metal base plate, at least one pair of lateral members extending longitudinally along the edges of said base plate, and a series of parallel rungs extending between said lateral members and connected thereto, the length of said rungs being substantially equal to one half the length of the wave to be delayed by the line, said lateral members being mounted so as to suspend said rungs between said base plate and said interaction space in spaced relationship to a side of said base plate facing said interaction space, said line being electrically equivalent to a chain of coupled circuits including Y both electrical coupling and magnetic coupling, and conducting means comprising at least one conducting member secured to said base plate near the central portion of said rungs, whereby a part of the lines of force of microwave electromagnetic eld is diverted to said member and said electrical coupling is reduced to a small value with respect to said magnetic coupling, said conducting memmember secured to said base plate near the central portion of said rungs, whereby a part of the lines of force of micro-wave electromagnetic field is diverted to said member and said electrical coupling is reduced to a small value with respect to said magnetic coupling, said conducting member having a surface arranged to be exposed to said electron beam propagated along said line on the side of said rungs opposite said base plate, said surface extending parallel to said rungs transversely of said delay line, as well as extending generally parallel to the locus of said rungs longitudinally of said line. i

2. A delay line as claimed in claim 1 wherein said conducting means comprises baflles extending between dimension of said baffles extending symmetrically on either side of the centers of said rungs.

3. A delay line as claimed in claim 1 whereinv said lateral members extend in a straight line.

4. A delay line as claimed in claim l wherein each lateral member is curved to circular shape in a plane perpendicular to the longitudinal direction of said rungs.

5. In a travelling wave tube comprising an envelope, a delay line for micro-waves inside said envelope, said delay line being so constructed and arranged as to interact with an electron beam propagated along said line in an adjacent interaction space and comprising a metal base plate, at least one pair of lateral members extending longitudinally along the edges of said base plate, and a series of parallel rungs extending between said lateral members and connected thereto, the length of said rungs being substantially equal to one-half the length of the wave to be delayed by the line, said lateral members being mounted so as to suspend said rungs between said base plate and' said interaction space in spaced relationship to a side of said interaction space, said line being electrically equivalent to a chain of coupled circuits including both electrical coupling* and magnetic coupling, and conducting means comprising at least one conducting member secured to said base plate nearthe central portion of said rungs, whereby a part of the lines of force of micro-wave electromagnetic eld is diverted to said member and said electrical coupling is reduced to a ber having a surface arranged to be exposed to said electron beam propagated along said line on the side of said rungs opposite said base plate, said surface extending parallel to said rungs transversely of said line as well as extending generally parallel to the locus of said rungs longitudinally of said line.

7. A micro-wave delay line comprising at least one metal base plate, a pair of lateral members essentially i parallel to said base plate and extending along the side said rungs and said base edges thereof and a series of essentially parallel rungs extending between the two lateral members and of a length approximating one-half the length of the wave to be delayed by the line, said lateral members being mounted so as to suspend said rungs exterior to one side-of said base plate, whereby a space is bounded by said base plate and said rungs, said line being electrically equivalent to a chain of coupled circuits including both electric-al coupling and magnetic coupling, and conducting means comprising a conducting'ller member secured to said base plate and extending in the space between said rungs and said base plate lengthwise of the delay lline for a distance greater than the distance between adjacent rungs, said ller member having a surface parallel to the locus of said rungs near the central'portion of said rungs, whereby y a part of the lines of force of a micro-wave electromagnetic iield is diverted to saidmember and said electrical coupling is reduced to a small value with respect to said magnetic coupling.

8. A micro-wave delay line comprising at least one metal base plate, a pair of lateral members essentially parallel to said base plate and extending along the side edges thereof and a series of essentially parallel rungs members and of a length approximating one-half the length of the Wave to be delayed by the line, said lateral members being so mounted as to suspend said rungs exterior to one side of said base plate, whereby a space is bounded by said base plate and said rungs, said line being electrically equivalent to a chain of coupled circuits including both electrical coupling and magnetic coupling, and conducting means including a filler member extending in the space between plate lengthwise of the delay line for a distance greater than the distance between adjacent rungs, said iiller member being in a symmetrical position relative to the centers of said rungs, and batlles extending between successive Vrungs and mountedon saidfiller member, the transverse dimension of said baes extending symmetrically on either side of the centers of said rungs, whereby a part of the lines of force of a micro-Wave electromagnetic field is diverted to said conducting means and said electrical coupling is reduced to a small value with respect to said magnetic coupling.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES 

